Numbers of fire-resistant construction materials are known and in common use. These construction materials are normally available in panel, preferably rigid panel, form so as to be useful as, or as a substantial portion of, common building parts.
These construction materials are relied upon to impart fire-resistance or fire-proofing in buildings and commonly replace, or partially replace, wood and similar flammable construction materials. Thus, for example, fire-resistant construction materials may be provided in panel form so as to constitute the structural facing of walls, ceilings, doors and the like.
It is also known to face these fire-resistant construction materials with a laminate, paint, or other cosmetic coating which may itself be either flammable or inflammable. In instances where a flammable facing or coating is applied to these fire-resistant construction materials, the construction materials serves as a fire-resistant barrier which provides insulation or separation of flammable building materials and thus also serves as a means of avoiding spread of flames in the event of fire.
A common example of the use of fire-resistant construction materials as a portion of a building material is in the core of a door. Such a construction is exemplified by U.S. Pat. No. 3,196,494 of Hartman et al, the disclosure of which is incorporated herein by reference. In such a door, the fire-resistant construction material constitutes its main structural support. The construction material itself need not be apparent, however, as it may be covered with, for example, a thin veneer of wood to give the appearance that the door is solid wood. Unlike solid wood, however, the door will not burn and will serve as a barrier for any fire which might occur on one side or the other.
One of the most common fire-resistant construction materials now in use comprises panels of a mixture of cement and asbestos. In such materials, the cement acts largely as an inert binder for the incombustible component, asbestos. Such construction materials, however, have serious disadvantages in use. They are extremely brittle and require special care in handling. Also, they cannot be nailed directly due to their poor impact strength. Accordingly, pre-drilling of holes is a necessity. Moreover, special tools must ordinarily be used to cut the panels and special molding, where they are mounted or otherwise fixed in position.
In Canadian Pat. No. 897,855 of Hartman, there is disclosed an improvement to the cement binder fire-resistant construction materials. That Canadian Patent describes structures in which incombustible components are dispersed and fixed into rigid panels with a two-part binder consisting of phenol formaldehyde resin and urea formaldehyde resin. Significantly, that invention overcomes many of the problems of special handling, brittleness, and low impact strength of fire-resistant construction materials containing cement.
Even the two-part binder system of this Canadian patent has not, however, met with complete success. In particular, the preparation of rigid panels from the fire-resistant construction material there described must be performed within a short period of time because of the limited pot life of the resin composition. Further, because water is required for the formation of such construction materials, difficulties with surface migration of salts such as certain incombustible components in the material have been encountered during the curing of the resin into a fixed panel. This migration may lead to an eventually heterogeneous composition and, by virtue of the surface location of such salts, may result in a panel in which important incombustible components may be only lightly bound and therefore are susceptible to loss through abrasion.